1. Field of the Invention
The present invention relates to a method of and an apparatus for producing raster data of an image including plural image parts, based on information of intersection points of scanning lines with contours of image parts.
2. Description of the Prior Art
Several efficient methods have been known for creating image data such as raster data of an image including plural image parts; for example, those described in Japanese Patent Laying-Open Gazettes No. Sho-59-101969, No. Sho-61-212895, and No. Hei-1-225989.
In the method disclosed in the Japanese Patent No. Sho-59-101969, a contour vector (closed loop vector) is obtained for each image part contained in a one-page-image and decomposed to element vectors. Here, each element vector data consists of coordinates of a start point and an end point, and indicates whether an image region below the element vector is a filling region or a non-filling region. The element vectors are sorted and merged according to predetermined rules and rearranged. Intersection points of the rearranged vector with scanning lines are obtained, and image data or run-length data are then produced corresponding to the coordinates of the intersection points.
In this first method, since each figure is processed based on its contour vector, intersection data is not required for each pixel on a one-page-image; thus, a memory capacity sufficient for processing is rather small.
The method of the Japanese Patent Sho-59-101969 has been improved to make a method disclosed in the Japanese Patent Hei-1-225989 which does not require sorting in a scanning direction; thus processing of the latter is much faster than that of the former.
In the first method, determining of contour vectors for all figures in a one-page-image, decomposing of the contour vectors into element vectors, and sorting and merging of the element vectors require rather long processing time, especially when a one-page-image contains a large number of figures. This becomes more serious because a character such as `A` or `1` is processed as a figure in this method. Provided that each character is defined by a hundred element vectors on average and a one-page-image contains two thousand characters, two hundred thousand vectors should be sorted and merged; this naturally requires a long processing time.
In the method disclosed in the Japanese Patent Sho-62-12895, information of intersection points of a figure contour with each scanning line is stored in a multi-digital memory for each pixel on a one-page-image. The intersection point information shows whether the intersection point is a filling start point or a filling end point on a scanning line. For example, when plural figure contours overlap one another at a particular pixel position and all the cross points thereon denote filling start points, the intersection point information at the pixel position is a positive multi-digital data indicating the number of overlaps. Image data or raster data are then produced on the basis of the intersection point information.
In this second method, since intersection point information is stored for each pixel on a one-page-image, additional processing is not required to determine intersection points of each contour vector with each scanning line in producing image data; thus processing of the second method is executed faster than the first method.
In the second method, improvement of the resolution of the one-page-image increases a memory capacity required for the multi-digital memory. For example, a one-page-image of 297.times.420 mm size with a resolution of 3000.times.3000 dpi needs a memory capacity of approximately 0.7 gigabyte.